<i>α</i> -Pinene nitrates: synthesis, yields and atmospheric chemistry

Abstract

Abstract. The biogenic volatile organic compound α-pinene is one of the dominant monoterpenes emitted to the Earth's atmosphere at an estimated rate of ~50 Tg C yr−1. Its atmospheric oxidation products in the presence of NO can lead to ozone production, as well as production of secondary organic aerosol (SOA). The major oxidation pathway of α-pinene is reaction with OH, which in the presence of NO can form either α-pinene nitrates or convert NO to NO2, which can photolyze to form ozone. In this work, we successfully synthesized four α-pinene hydroxy nitrates through three different routes, and have identified these 4 individual isomers in α-pinene/OH/NO reaction chamber experiments. From the experiments, we determined their individual production yields, estimated the total RONO2 yield, and calculated the relative branching ratios of the nitrate precursor peroxy radicals (RO2). The combined yield of the four α-pinene nitrates was found to be 0.130 (±0.035) at atmospheric pressure and 296 K, and the total organic nitrate yield was estimated to be 0.19 (+0.10/−0.06). We also determined the OH rate constants for two of the isomers, and have calculated their overall atmospheric lifetimes, which range between 22 and 38 h.